Tunneling in the Reactions of Carbenes and Oxacarbenes

Gerbig, Dennis; Schreiner, Peter R.

doi:10.1002/9781118730379.ch7

Cited by 7 publications

(4 citation statements)

References 110 publications

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“…40 Methylhydroxycarbene is not a singular case in the new family of hydroxycarbenes, a long-elusive class of molecules (Figure 4). 41 Indeed, we found tunneling control to prevail for tert-butyl-, 42 phenyl-, 43 cyclopropyl-, 44 and trifluoromethylhydroxycarbene 45 by giving the thermodynamic products from [1,2]H-shift tunneling reactions of large but narrow barriers similar to the depiction of Figure 2. It is comforting to see that the tunneling half-lives well with the stereoelectronic properties of the R group and that they very sensitively depend on the absolute barrier height (assuming that the all barriers have very similar overall shapes).…”

Section: ■ Emergence Of Tunneling Controlsupporting

confidence: 59%

Tunneling Control of Chemical Reactions: The Third Reactivity Paradigm

2017

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This Perspective describes the emergence of tunneling control as a new reactivity paradigm in chemistry. The term denotes a tunneling reaction that passes through a high but narrow potential energy barrier, leading to formation of a product that would be disfavored if the reaction proceeded by passage over kinetic barriers rather than through them. This reactivity paradigm should be considered along with thermodynamic and kinetic control as a factor that can determine which of two or more possible products is likely to be the one obtained. Tunneling control is a concept that can provide a deep and detailed understanding of a variety of reactions that undergo facile (and possibly unrecognized) tunneling.

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Section: ■ Emergence Of Tunneling Controlsupporting

confidence: 59%

Tunneling Control of Chemical Reactions: The Third Reactivity Paradigm

2017

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“…Cryogenic matrix isolation techniques were used to investigate the ring expansion of fluoro(1-methylcyclobut-1-yl)carbene ( 11 ) to cyclopentene 12 (Scheme ). − Carbene 11 was chosen instead of 1 to study 1,2-C atom shifts for two main reasons. The CH 3 -group on its C1′ atom avoids a potentially competitive 1,2-R group shift; CH 3 -groups have a low migratory aptitude. , Additionally, the F atom lowers Δ E S–T (i.e., Δ E S–T ≪ 0 kcal/mol), so unwanted chemistry from higher-energy 3 11 is avoided.…”

Section: Resultsmentioning

confidence: 99%

Bent Singlet Cyclobutylcarbene: Computed Geometry, Properties, and Product Selectivity of a Nonclassical Carbene

Rosenberg

Brinker

2019

J. Org. Chem.

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Ab initio computations of cyclobutylcarbene (c-C 4 H 7 CH) were performed using the UMP4(fc)/6-311++G(2df,2p)//UMP2(full)/6-311++G(d,p) theoretical model. The carbene's most striking feature is its :CH-group. It is markedly bent toward the elongated C1′−C2′ bond in the singlet ground-state but not in the triplet state, which is at least 1.1 kcal/mol higher in energy. Nonclassical 3C2E bonding among the C1, C1′, and C2′ atoms is prominent in the HOMO{−1}. The electron-donating ability of the nonbonding HOMO is thereby enhanced. The intensified nucleophilicity of the singlet carbene is manifested in quantifiable ways. For example, its hard and soft acid and base (HSAB) hardness, HSAB absolute electronegativity, and gas-phase proton affinity rival those of ylide-stabilized Nheterocyclic carbenes. It is computed to act as a nucleophile toward alkenes with higher HSAB hardness values. Transition states from singlet cyclobutylcarbene to bicyclo[2.1.0]pentane, cyclopentene, and methylenecyclobutane were computed and confirmed by intrinsic reaction coordinate calculations. Activation energies depend on the singlet's conformation with regard to c-C 4 H 7 ring-puckering, :CH-group rotation, and :CHgroup bending. The singlet's bent :CH-group favors bicyclo[2.1.0]pentane and cyclopentene formation.

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“…But, during the optimization process of both carbenes and vinylidenes, if R, R', R" is CH3, then a 1,2-hydrogen shift [27] occurs and the optimized structure is an olefin. In two vinylidenes, (CH3)2C=C: and (NH2)2C=C:, the S optimization leads to structures where the terminal carbon approaches the substituent (CH3 or NH2).…”

Section: Resultsmentioning

confidence: 99%

The Hydrogen-bond Basicity of Carbenes

Abraham¹,

Elguero²,

Alkorta³

2018

Croat. Chem. Acta

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Abstract:We have evaluated theoretically in the gas-phase (MP2/aug-cc-pVTZ) the hydrogen-bond basicity of simple carbenes and vinylidenes and compared them to the corresponding nitrogen and oxygen derivatives using HF as Lewis acid. These values fit conveniently with B values only if sp 3 and sp 2 atoms are treated separately, which is a consequence of the gas-phase (calculated) vs. solution (measured) effects.

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Tunneling in the Reactions of Carbenes and Oxacarbenes

Cited by 7 publications

References 110 publications

Tunneling Control of Chemical Reactions: The Third Reactivity Paradigm

Tunneling Control of Chemical Reactions: The Third Reactivity Paradigm

Bent Singlet Cyclobutylcarbene: Computed Geometry, Properties, and Product Selectivity of a Nonclassical Carbene

The Hydrogen-bond Basicity of Carbenes

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